1. Field of the Invention
The present invention relates to the field of semiconductor integrated circuit (IC) manufacturing, and more specifically, to a method of and an apparatus for venting a pellicle cavity of a mask.
2. Discussion of Related Art
The manufacturing of IC devices involves the formation and removal of various materials from a wafer. Photolithography is a process that uses exposure to radiation followed by developing to print a pattern from a mask in a photoresist coating on the wafer. A binary mask is a type of mask that only modulates the amplitude of the radiation. Etch is a process that transfers the pattern from the photoresist coating to the wafer. A layer may be considered critical if it includes a feature that is designed with a very small critical dimension (CD). Critical layers typically include the isolation, gate, contact, and first metal layers.
When the CD of the feature for a critical layer becomes smaller than the wavelength of the radiation, the resolution of the aerial image of the feature may be degraded by diffraction which is a spreading of the radiation. A phase-shifting mask (PSM) is a type of mask that modulates the phase as well as the amplitude of the radiation so as to minimize the detrimental effects of diffraction.
Optical proximity correction (OPC) may be incorporated into the design of a mask to compensate for systematic distortion of the image from print or etch. The distortions may include corner rounding, line shortening, and CD offset between isolated features and nested features.
A mask for a critical layer, such as a PSM with OPC, must be kept clean of environmental contamination in order to ensure fidelity of the pattern transfer. A mask may be kept clean by covering it with a pellicle mounted on a frame. However, a change in the ambient atmosphere may create a pressure differential between the inside and the outside of the pellicle cavity.
Thus, what is needed is a method of and an apparatus for venting a pellicle cavity of a mask.